Method of producing solid solutions of the carnallite type



tion.

United States Patent G 3,312,607 METHOD OF PRODUCING SOLID SOLUTIONS OF THE CARNALLITE TYPE Robert I). Goodenough, and Remigius A. Gaska, Midland, and Richard C. Belski, Bay City, Mich., assignors to The Dow Chemical Company, Midland, MiclL, a corporation of Delaware No Drawing. Filed Nov. 4, 1963, Ser. No. 321,332 4 Claims. (Cl. 20470) The invention relates to a method of producing solid solutions of the carnallite type and, more particularly, is concerned with the production from brines of carnallite compounds corresponding to the empirical formula MgCl -xKCl-yNH Cl- 6H O, wherein the sum of the mole fractions of x(KCl) and y(NH Cl) is equal to the number of moles of MgCl In the manufacture of magnesium by electrolysis of magnesium chloride, certain magnesium reduction cells require the presence of a fixed amount ofpotassium chloride in the anhydrous magnesium chloride cell feed. The method of this invention allows one to prepare a solid solution of MgCl -xKCl-yNH Cl-6H O containing the desired fixed weight ratio of magnesium chloride to potassium chloride. The actual cell feed may be prepared by desiccation of the waters of hydration and sublimation of ammonium chloride'from the compositions of the present invention.

It is an object of the instant invention to provide a method for producing a solid solution of containing a desired fixed weight ratio of magnesium chloride to potassium chloride for eventual use as a cell feed in magnesium reduction cells.

Other objects and advantages of the instant invention will become apparent from reading the detailed description disclosed hereinafter.

It has been discovered that magnesium chloride can be effectively separated from sodium, calcium, potassium, lithium and/or strontium containing brines in the form of a composition corresponding to the epirical formula MgCl -xKCl-yNH Cl-6H O by adding ammonium chloride to such brines. The mole ratio of potassium chloride to ammonium chloride in the solid solution is controlled directly by the amounts of ammonium chloride added. This enables one to arrive at a definite product composi- Using this technique, it is possible to recover magnesium chloride effectively from brines containing as little as 4 to 5 percent MgCl and other salts.

In carrying out the method, solid ammonium chloride is added to a brine solution so as to give a weight ratio of ammonium chloride to magnesium chloride within the range of from about 0.28 to 1.7 and a weight ratio of ammonium chloride to potassium chloride within the range of from about 0.63 to about 3.8 thereby to precipitate MgCl -xKCl'yNH Cl-6H O. In general, in the practice of the methodthe weight ratio of magnesium chloride to potassium chloride should be within the range of from 1.9 to 7.15. The upper limit of this range, i.e., 7.15 applies when the solution is mutually saturated with respect to both magnesium chloride and potassium chloride at 35 C. However, when the solution is not saturated with respect to potassium chloride, the upper limit will be higher than 7.15. The mixture is then heated to temperatures within the range from about 50 to about 95 C. to dissolve all the ammonium chloride and then cooled preferably to room temperature or lower. The precipitate is then filtered and dried, e.g., at a drying temperature of 7080 C. for a period of about 8 to about 18 hours.

If the precipitate of MgCl -xKCl-yNH CL6H O is re- ICC moved from the brine solution at a temperature lower than room temperature (e.g. 10 C.) the recovery of increases. Recovery of the precipitated product at a temperature higher than room temperature (e.g., 35 C.) decreases recovery of the product.

In one variation of the method of the instant invention, a brine containing magnesium chloride, potassium chloride, calcium chloride, sodium chloride, lithium chloride and strontium chloride is evaporated, normally at its boiling point, in order to concentrate the brine solution with respect to magnesium chloride whereby a precipitation of the complex MgCl -xKCl*yNH Cl-6H O occurs on addition of ammonium chloride to said solution.

In practice, the magnesium chloride content of the brine needed to provide for precipitation of.

upon addition of ammonium chloride varies with the calcium salt content of the brine solution (e.g., from about 2 to about 38 weight percent calcium chloride). To illustrate, at a reaction temperature of about 35 C., e.g., brines with high calcium salt content (e.g., from 2538 percent by weight) compensate for a low anagnesium chloride content (e.g., as low as 4 percent by weight MgCl content) and assure precipitation of the product with ammonium chloride. When the concentration of calcium salt is low (e.g., from 0 to about 25 percent) a higher MgCl concentration (e.g., from about 27.0 to about 9.5 percent) is necessary to initiate precipitation of MgCl -xKCl-yNH Cl-6H O from the brine solution on the addition of ammonium chloride thereto.

It is to be understood that these data are for one temperature range, i.e., 35 C., other temperatures may require slightly different concentration proportions. At a lower temperature, less magnesium chloride is required; at a higher temperature more magnesium chloride will be required to achieve the desired precipitation.

The ammonium chloride should be in solid form for use in the method of the instant invention, however, the degree of particulation is not important.

Variation of the pH of the initial brine solution (e.g., from 1 to 6) does .not have any significant efiect on the results of the instant method.

The following example further illustrates the invention, but is not to be construed as limiting the invention thereto.

EXAMPLE About 15 grams of ammonium chloride were added to about 200 grams of a brine having a specific gravity of 1.37 and a pH value of 3.5 and a composition on a weight basis as follows:

Constituent: Weight percent Potassium chloride 2.37 Sodium chloride 0.55 Calcium chloride 29.00 Strontium chloride 0.70 Lithium chloride 0.078 Magnesium chloride 4.80 Water (by difference) about 62.50

The entire mixture was then heated to C. to dissolve the ammonium chloride and then cooled to 25 C. 30.4 grams of precipitate was formed. This precipitate was separated from the solution by filtration and dried at 60 C.

25.7 grams of dry precipitate was obtained. This was solid solution of found to have the following composition on a weight percent basis:

Water (by difference) about 36.33

Calcium chloride, sodium chloride, and part of the potassium chloride not chemically bound to and in the MgCl -xKCl-yNH Cl-6H O may be removed by washing with the precipitate. Through X-ray diffraction and chemical analysis it was proved that the precipitate, less the above impurities, was the solid solution of MgCl -xKCl-yNH Cl- 6H O.

Various modifications may be made in the present invention without departing from the spirit or scope thereof for it is to be understood that we limit ourselves only as defined in the appended claims.

We claim:

1. The method of producing a solid solution of wherein the sum of the mole fractions of x(KCl) and y(NI-I Cl) equals the number of moles of MgCl from a brine solution containing magnesium chloride and potassium chloride in a weight proportion of at least 1.9 which comprises:

(a) adding solid ammonium chloride to the brine solution, the amount of said ammonium chloride providing a weight proportion of NH Cl/KCl in said solution within the range of from about 0.63 to about 3.8 and a weight proportion of the in said solutionwithin the range of from about 0.28 to about 1.7;

(b) precipitating MgCl -xKCl-yNH Cl'6H O product therein wherein the sum of the mole fractions of x(KCl) and y(NH Cl) equals the number of moles of MgCl and (c) thereafter separating the precipitation product from the residual solution.

2. The method in accordance with claim 1 wherein *5 said brine contains from about 2 to about 38 weight percent calcium chloride and from about 4 to about 27 weight percent magnesium chloride.

3. The method of producting a solid solution of.

MgCl xKClyNH Cl 6H O wherein the sum of the mole fractions of x(KCl) and y(NH Cl) equals the number of moles of MgCl from a brine solution containing at least 4 percent magnesium chloride and potassium chloride which comprises:

(a) adding solid ammonium chloride to the brine solution, the amount of said ammonium chloride providing a weight proportion of NH cl/KCl in said solution within the range of from about 0.63 to about 3.8 and a weight proportion of the NH Cl/MgCl in said solution within the range of from about 0.28 to about 1.7;

(b) heating the mixture of ammonium chloride and brine solution to a temperature within the range of from about to about C. to dissolve substan tially all the ammonium chloride;

(0) cooling said mixture to about 25 C. thereby substantially completing precipitation of wherein the sum of the mole fractions of x(KCl) and y(NH Cl) equals the number of moles of MgCl (d) separating said precipitate of from the said solution; and (e) drying said precipitate of thereby producing a solid solution of MgCl xKCl yNH Cl- 6H O 4. The method in accordance with claim 3 wherein said brine contains from about 2 to about 38 weight percent calcium chloride.

References Cited by the Examiner UNITED STATES PATENTS 1,301,766 4/1919 Wallace 23-91 1,875,013 8/1932 Kaselitz 23 s7 2,974,093 3/1961 Bauer et al 23-437 3,181,930 5/1965 Olsen 23-91 HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

1. THE METHOD OF PRODUCING A SOLID SOLUTION OF 